Recovery of dicyanodialkyl ethers and sulfides used as solvents in an aromatic hydrocarbon extraction process



Sept. 18, 1951 C, MEDCALF ETAL 2,568,159

RECOVERY OF DICYANODIALKYL ETHERS AND SULFIDES USED AS SOLVENTS IN- ANAROMATIC HYDROCARBON EXTRACTION PROCESS Filed Feb. l0, 1950 H547[KCA/#M6547 3.

INVENToRs {06f-Ami C. Mf C44 F, Fenu .0 W//,4 5/560,

ATTORNEY Patented Sept. 18, 1951 Stdt , RECOVERY or v DICYANODIALKYLETHERS AND sULFmEs USED As soLvENTs IN AN ARoMArIe HvDRocARBoNEXTRACTION PROCESS `I'Ziugene C.Mdcalf,` Bound Brook, and William E.Siseo, Somerville; N. J., assignors to American (Ilyarlarnid Company,New York, N. Y., a corporation of Maine Application February 10, 1950,Serial No. 143,5785

This invention relates to an improved method of recovering solvents ofthe bis-cyanoalkyl ether and sulde type.

Bis-cyanoalkyl ethers and suldes, particularly the beta-cyano-ethylether and sulde, have shown extraordinarily good solvent characteristicsfor the separation of unsaturated hydrocarbons from saturatedhydrocarbons; e. g, aromatics from parans and the like, and permit avery effective process of solvent refining of hydrocarbon fractions,particularly those obtained in the petroleum industry. The ethers andsulfldes show a very high solubility for aromatic hydrocarbons, such asbenzene, toluene, naphthalene and the like, and extremely low solubilityfor parafns. It is thus possible to use the solvents very effectively inseparating aromatic compounds from parafns.

Solvent processes using cyanoalkyl ethers and sulfides present a seriousproblem of solvent recovery. In the past the solvents have beenrecovered by various distillation processes. However, the high boilingpoints of the cyanoalkyl ethers and suldes result in seriousdecomposition which may amount to as high as 10 to 30%- per hour attemperatures of 200 C. and higher. For many processes this loss resultsin a prohibitive cost and has seriously restricted the eld of utility ofthese otherwise extraordinarily effective solvents.

The present invention depends on the discvery that it is possible torecover almost quantitatively the solvents by use of water. The.solubility curve of the solvents in Water is extraordinarily steep. Attemperatures of about 75 to 100 C. bis(2-cyanoethyl)ether and Water aremiscible in all proportions and the solubility of the sulfldes issuiciently high for practical use. At room temperature, however, thesolubility drops to not more than a very few per cent even for the mostsoluble liquids. In fact, the solubility is so low that the amount ofwater dissolved in the solvent at room temperature is small enough thatit does not interfere with the action of the solvent on reuse.

The recovery of the solvent is very high, and

there is practically no loss by decomposition asl the temperature neednever exceed 100 C., and even in the presence of water the solvents aresubstantially stable. The cost of the process is very low because thewater can be reused and therefore introduces no loss in dissolvedsolvent, and the heat requirements of the process are low.

It is a further advantage that the Water-solvent solution Contains onlya fraction of a percent of the dissolved aromatics, and even this smallpercentage is not lost because it is carried around through the processWhen the solvent is reused.

rhe Vpresent invention is not limited to any particular steps whichresult in a solution of unsaturated and, particularly, aromaticcompounds in the solvent. The most important field, however, is inconnection with the solvent separation of petroleum fractions, and thecheap solvent recovery system which is made possible by the presentinvention for the rst time opens up a large eld to solvent recoveryprocesses using the cyanoalkyl ethers and sulildes as solvents.

The solvents areY also useful forr the separation of compounds otherthan hydrocarbons Where there is a suicient difference in solubility.`For example, they may be used in the separation of monoalkyl phenolsfrom polyalkyl phenols, N- monoalkyl aromatic amines from N-polyalkylaromatic amines, N-alkyl aromatic amines from isomeric Cealkyl aromaticamines, and the like. The present .process of solvent recovery is notparticularly concerned with the material which is dissolved in thesolvent so long as it is not water-soluble. The invention will bedescribed more particularly in connection Withrsolutions of aromatichydrocarbons in the solvents, it being understood that the mechanism ofthe separating process is no diierent with solutions of aromatichydrocarbons than with solutions of the other materials referred toabove. Y

While the present invention is particularly suitable for the recovery ofbis (Z-cyanoethyD- ether and sulde', it is not limited thereto, and isequally effective with other cyanoalkyl ethers and suldes, such as thebeta and gamma-propyl compounds, butyl, etc. As the hydrocarbon chainlengthens, a pointl is finally reached where the solubilitycharacteristics in Water are no longer satisfactory for separation, andwhere the compounds are not liquid at room temperature. The invention istherefore limited tothe recovery of the lower cyanoalkyl ethers andsuldes.

The invention will be describedV in greater detail in conjunction withthe following specic examples and with the drawing, which is adiagrammatic' flowsheet of a typical embodiment of the invention.

In order to make the drawing more clear, the cyanoalkyl ether andsulfide solvents will be designated by the letter S, andwater-insoluble, unsaturated materal, such as aromatic hydrocarbons, bythe letter A. The general ovvsheet will be described rst, followed byspecic examples giving proportions.

In the drawing, the solution of the aromatics in the solvent is heatedto 85 C. in the steamheated heater I. The hot liquid is then introducedinto an extraction column near the top at point 2. The whole of thecolumn is maintained at about 85 C. Water containing a very small amountof solvent is introduced into the bottom of the extraction column at thepoint 4, and iiows up, becoming gradually saturated with solvent,leaving at point 6, while a very concentrated solution of thearomatics-in-solvent, or solvent-inaromatics, ows out through the bottomof the column at 5. The solution of solvent in water next passes throughthe heat-exchanger 3, where it is cooled by heat exchange with watercontaining a small amount of solvent, the latter being heated up andreintroduced into the extraction column at point 4, as described above.In the heat-exchanger the solution of solvent in water is cooled toslightly above room temperature, about 25 C., and ows into a decantingvessel 1, where two layers form, the upper layer being water containinga small percentage of solvent, and the bottom layer solvent containing asmall percentage of water. The two layers are continuously decanted, thewater layer passing to a receiver 9 from whence it is recirculatedthrough the heat-exchanger 3. The solvent layer goes to a receiver 8from which it can be reused in the original process producing thesolution of aromatics.

Example 1 'I'he process shown on the iiowsheet is carried out using asolution of 1 part of naphthalene in 10 parts of bis(2cyanoethyl) ether.Hot water, containing a small amount of solvent, is introduced into thebottom of the extraction column at a rate about three times that of thesolvent introduction at the top of the column. A raiilnate, consistinglargely of naphthalene having dissolved in it a little solvent, leavesthe bottom of the column. The small amount of solvent can be removedtherefrom by washing with hot water or other simple means. Thewater-solvent layer leaving the top of the column contains only about0.3% naphthalene. When this solution is cooled, it separates into twolayers, the water layer containing very little solvent, about 10%, andthe solvent layer carrying the naphthalene likewise contains a smallamount, about 10%, of water. The water is recycled through theextraction column with any make-up water added, and the solvent can bereused in the separation of naphthalene in petroleum fractions. 'Ihevery small amount of water dissolved in the solvent does not materiallychange its solvent characteristics and makes it unnecessary to removethe water, although, if desired, this can be done by a fairly lowtemperature distillation.

Example 2 Ihe procedure of Example 1 is followed in general, but thesolvent is bis(2cyanoethyl)suliide instead of the ether of Example 1.The solubility characteristics of the sulfide are such that the waterratio should be higher, about 12 to 1 instead of 3 to 1 as in Example 1.Also, the temperature in the column may advantageously be slightlyhigher, about 90V C. The distribution of naphthalene in various layersis practically the same as in Example 1. The decanted water containsabout 1% of the solvent, and the Solvent about 1% of water.

4 Example 3 The procedure of Example 1 is followed, but the solventcontains toluene instead of naphthalene. The column is operated ataslightly lower temperature, about C. The separation is substantially thesame as in Example 1, except that the circulation in the column isreversed; toluene coming off the top and the water-solvent mixturecoming oif the bottom.

Example 4 3 parts of water and 1 part of a solution of 10% naphthalenein bis(2cyanoethyl) ether is thoroughly mixed and heated to C., is thenallowed to settle hot, a smaller, lower layer separating out. This isdecanted and, on cooling, solidi-lies. It contains about 40%naphthalene. The Watersolvent layer contains about 0.3% naphthalene and,on cooling, separates into two layers in the same manner as thewater-solvent mixture in Example 1.

Example 5 A mixture of 3 parts of water and 1 part ofbis(2cyanoethy1)sulide containing 10% of toluene is heated to 80 C. andmixed, and is then allowed to settle. A small upper layer comes off,containing solvent with about 30% of toluene. The lower, water layercontains about 0.3% toluene and, on cooling, separates as described inExample 3.

Example 6 The procedure of Example 1 is followed, but the solution isone of naphthalene in alpha, beta dicyano diethylether. This ether hassomewhat less water solubility than the solvent of Example 1, and theproportion of water should therefore be 10 to 1 instead of 3 to l. Thetemperature in the hot column is 85 C. The raiiinate which is removedfrom the bottom of the column contains 30 to 35% of naphthalene.

Example 7 The procedure of Example 1 is applied to a 12% solution ofnaphthalene in bis(betacyano isopropyDether. The extraction is effectedat 85 to 90 C. with Water saturated with solvent. The ralinate containsabout 30 to 35% naphthalene and the water and solvent layers, whichseparate on cooling, contain from 4 to 6% of water and solventrespectively, instead of about 10% as in the case of Example 1.

In some of the examples a proportion of 3 parts of water to 1 part ofsolvent has been used. The proportion is in no sense critical, butrepresents a good economical lower limit with the more soluble solventssuch as the ether of Example 1. More water may, of course, be employed,and is needed where the solubility is lower, i. e. some of the sulfides.Unnecessary water, however, only increases the circulating load on theequipment. A somewhat smaller amount of water can also be used, but ifthe amount is cut too small the efficiency of separation sometimessuffers, resulting in more solvent in the aromatios separated, and it istherefore desirable to operate with a slight excess of Water.

The examples describe processes which are efiected substantially atatmospheric pressure. For most operations this is preferable because iteiects a substantial saving of equipment. On the other hand, it ispossible to operate the extraction column in the case of continuousprocceses. Q1 the mixing vessel in the case of batch processes, undermoderate pressure. This can result in somewhat higher temperature of thewater and has the advantage in some cases of preventing vapor lock orlosses where the dissolved material has a considerable vapor pressure atthe temperature used in the extraction. Even with pressure it isnormally not necessary to go to temperatures higher than '70 to 100 C.and, in fact, it is usually desirable to maintain as low a temperatureas is consistant with good solvent recovery.

We claim:

1. A process of separating dissolved material of W water solubility fromsolutions in a dinitrile solvent having the formula alkCN in which X isan element of the sixth group of the periodic system, having an atomicnumber not exceeding 16, and alk is a lower alkylene radical, whichcomprises mixing the solution with water at a temperature of about 70 to100 C., the amount of water being suiiicient to disai..

2. A process according to claim 1 in which the hot water is contactedwith the solvent in the form of a counter-current stream and theseparation of the water-insoluble layer from the unitary water-solventlayer is effected continuously.

3. A process according to claim 2 in which the dissolved materialbelongs to the class of aromatic hydrocarbons.

4. A process according to claim 3 in which X is oxygen.

5. A process according to claim 4 in which the solvent isbis(2cyanoethyl) ether.

6. A process according to claim 5 in which the hydrocarbon isnaphthalene.

7. A process according to claim 1 in which X is oxygen.

8. A process according to claim 7 in which the solvent is bis(Z-cyanoethyl) ether.

9. A process according to claim 1 in which X is sulfur.

10. A process according to claim 9 in which the solvent isbis(2cyanoethyl) sulde.

EUGENE C. MEDCALF. WILLIAM E. SISCO.

REFERENCES CITED The following references are of record in the le ofthis patent:

.UNITED STATES PATENTS Number Y Name Date 2,433,751 Friedman Dec. 30,1947 2,439,534 Wilkes Apr. 13, 1948 2.441.827 McKrlniS i- 1 May 18, 1948

1. A PROCESS OF SEPARATING DISSOLVED MATERIAL OF LOW WATER SOLUBILITYFROM SOLUTIONS IN A DINITRILE SOLVENT HAVING THE FORMULA